1. Field of the Invention
The present invention relates to a frame using a length of high-tension thread for fastening a lens in each half-rim, and more particularly to the fastening structure, of the high-tension thread to each end of the half-rim.
2. Related Arts
An eyeglasses frame of the type to which the present invention can be applied has a pair of parts each comprising a half-rim and a length of thread stretched between the opposite ends of the half-rim, holding a lens between the stretched thread and the half-rim. Such half-rimmed glasses are light, significantly widening the field of sight. As seen from FIG. 9, a most popular frame of such type comprises two circular-arc rims "a" connected by an intervening bridge "d", a length of thread "b" stretched between the opposite ends of each circular-arc "a" to hold the lens "c" between the circular-arc rim "a" and the stretched thread "b". Each circular-arc rim "a" has a rectangular shape in cross-section. The half-rim has a joint piece "e" integrally connected to its outer edge, and a temple is hinged to the joint piece "e", thereby permitting the temple to be folded on the front.
FIG. 10 shows an enlarged cross section taken along the line 10--10 in FIG. 9. As seen from the drawing, the half-rim "a" has a groove made on its inner side whereas the lens "c" has a groove made on its outer circumference. The lens "c" is fixed to the half-rim "a" by inserting a flexible cocoon-shaped piece "f" into the confronting grooves of the lens and the half-rim "a".
FIG. 11 shows how the length of thread "b" is fixed to each end of the half-rim "a". The half-rim "a" has two holes made in each end. Each hole is 0.7 millimeters in diameter, and the two holes are separated 1.5 millimeters apart from each other. Each end of the thread is inserted into these holes as shown in FIG. 11(a). The lens is fitted in the space defined by the half-rim and the thread "b", to which the stretch of 1 to 3 kilograms is applied. The thread "b" is apt to invaginate in the groove "g" of the half-rim "a", so that the thread "b" is caught by the groove "g" as shown in FIG. 11(b). Although the thread "b" cannot be slipped off from the holes, the thread "b" can be often cut and broken by the sharp edge "h" of the circumference of the hole.
FIG. 12(a) shows another form of wire half-rim. FIG. 12(b) is a perspective view of the end of the half-rim. The half-rim is called "T-type rim", which requires no joint such as the flexible cocoon-shaped piece "f". It has projection "i" extended along the inner circumference of the rim and the projection "i" is fitted in the circumferential groove of the lens. The end of the half-rim has two holes "j" made therein. Each end of the thread is inserted in these holes "j". The thread, therefore, is apt to be cut and broken there when it is stretched, as is the case with the half-rim described above with reference to FIG. 11.
FIG. 13 shows a wire half-rim to be fitted in the circumferential groove of the lens. FIG. 13(a) is a cross-section of the lens, showing how the wire half-rim is fitted in the circumferential groove of the lens. FIG. 13(b) is a perspective view of the end of the half-rim. The half-rim fitted in the circumferential groove of the lens is invisible, giving a slim shape to the eyeglasses. As seen from FIG. 13(b), the half-rim has a joint piece "k" soldered to its end, and the joint piece "k" has two holes "j" made therein. Each end of the thread is inserted in these holes "j". The thread, therefore, is apt to be cut and broken there when it is stretched, as is the case with the half-rim described above.
The thread to be used in such a frame is 0.52 millimeters thick, and it has a stretch strength of approximately 10 kilograms. The conventional thread-fastening structures allow the thread to be broken when being subjected to the stretch of approximately 3.6 kilograms, much smaller than the inherent stretch strength of the thread.
FIG. 14 shows still another example of fastening structure (see Japanese Patent Application No. H-9-250091). As shown in the drawing, the thread "b" has a loop "l" formed on each end whereas the half-rim has a hook "m" formed on each end. Each loop "l" of the thread "b" is caught by the associated hook "m" of the half-rim. As seen from the enlarged view of FIG. 14(b), the thread "b" has its folded end crimped by an associated sleeve "n", which has its inner surface knurled. With this arrangement the thread can be resistive to the stretch of approximately 8.4 kilograms. As seen from FIG. 15, the thread has two loop ends at its opposite ends, leaving a predetermined length therebetween. This configuration, however, prevents the adjusting of the loop-to-loop length to tightly encircle a selected lens.
After grinding and reshaping lenses in the eyeglasses shop the so reshaped lenses are fitted in the half-rimmed frame by making the loops of such predetermined length of threads to be caught by the hooks of the half-rims of the front. If the predetermined length of thread is too long, the lens is apt to slip off from the front. Conversely, if the predetermined length of thread is too short, the lens cannot be held in the front. If the thread is stretched around the lens by force to be caught by the hooks of the half-rim, the lens and/or the thread is subjected to a destructive force, thus breaking the lens or thread.